Implantation of an artificial vessel into a living body first causes primary thrombi to grow on the inner surface thereof which is in contact with blood, and cells propagate themselves thereon to form a neointima, which becomes an antithrombotic intimal tissue. Thus, it is not until the inner wall of the artificial blood vessel is vitalized that the artificial blood vessel can play a role as a substitute for the living blood vessel.
The artificial blood vessel is also required, in view of performance in operations, to have a property of being readily pierced with a suturing needle when anastomosed to a living blood vessel. On the ether hand, puncturing is frequently repeated in blood access for hemodialysis, which is used for connecting arteries and veins. Therefore the vessel wall is required to be durable to repeated puncturing to prevent it from forming a hematoma induced by bleeding after puncturing and to have blood impermeability to prevent formation of seroma due to serum penetrating through the vessel wall. The term "blood impermeability" used herein means that the porosity (amount of leaked water/cm.sup.2 .multidot.min.multidot.120 mmHg) is substantially zero.
Japanese Provisional Patent Publication (KOKAI) No. 60-182959/1985 discloses an artificial blood vessel made of an elastomer having a reticular structure containing pores (1 to 100 .mu.m) over the entire thickness, from the inner surface to the outer surface, of the vessel wall. It is described that the reticular structure containing pores which penetrate the vessel wall from the inner surface to the outer surface allows organization of the artificial blood vessel to proceed rapidly and stably when implanted in a living body.
In this type of artificial blood vessel, immobilization of the intimal tissue depends on the so-called anchor effect, i.e. intrusion of the intimal tissue into the pores of the reticular structure. However, such intrusion and growth of the intimal tissue cannot be achieved to a sufficient depth, so that a high anchor effect cannot be expected. Moreover, the pores penetrating through the vessel wall inevitably cause hyperplasia, making immobilization thereof more difficult.
The above patent literature also discloses that the surface of the artificial blood vessel which is brought into contact with blood, i.e. the inner surface of the blood vessel, may be coated with albumin, gelatin, chondroitin sulfate or heparin-containing material for the purpose of improving the antithrombotic property of the artificial blood vessel at the initial stage of implantation to a living body. It is true, however, that the antithrombotic property of the artificial blood vessel at the initial stage of implantation can be improved by this method, but the intimal tissue is prevented from intruding into the pores to show poor adhesion and peels off easily. Thus, the peeled intimal tissue further grows to form pannus which blocks the bloodstream, and in turn causes to form thrombi.
Japanese Provisional Patent Publication (KOKAI) No. 62-25866/1987 discloses an artificial blood vessel made of a porous material, the pores in which a gelatin crosslinked with diisocyanate are filled by impregnation. The gelatin decomposes in a living body to allow new tissue to grow into the porous material. In the artificial blood vessel disclosed in the above patent literature, the optimum decomposition rate of the gelatin is decided depending on the balance between the speed of tissue intrusion or growth and the degree of freedom from blood leakage through the vessel wall having communicability. However, there is a wide individual difference in the growth speed of the neointimal tissue, and it is impossible to decide the balance uniformly. And thus, it is difficult to allow the artificial blood vessel to have a property of vessel wall matched with the individual difference.
Japanese Provisional Patent Publication (KOKAI) No. 61-185271/1986 discloses an artificial blood vessel consisting of an elastomeric porous material forming the structure of the blood vessel and a tubular material made of a fiber which is present in contact with or bonded to some parts of the porous material. However, the pores present in the porous material in this artificial blood vessel communicate with one another from the inner surface to the outer surface, so that the serum penetrates through the vessel wall after implantation to a living body and leaks out of the vessel wall and is thus liable to form a seroma. The pores communicating throughout the vessel wall are liable to be cracked or expanded by the creep induced by pulsation repeated for a long time, leading to the fear of aneurysmic expansion or rupture. Further, the above artificial blood vessel suffers a problem that when it is used for hemodialysis, it is liable to form a hematoma or to be infected by the bleeding through the holes formed by puncturing, so that its durability will notably be reduced by repeating such localized puncturing for a long time.